The stator coil end windings of the conductors of a turbine generator typically extend axially from the stator core structure for a significant distance. The straight segments of the conductors are disposed in the stator core slots such that they are supported by the slots, however, the end windings extend outward from the slots a significant distance such that they are not adequately supported by core slots. Thus, the end windings are subject to severe vibrations and stress, as well as the influence of their own weight, during operation. Adverse structural deformations can be caused by mechanical vibrations during normal operations or the very large electromagnetic forces which occur during abnormal short-circuit or fault conditions.
Normally, each individual conductor is braced to its associated conductors to form a conically shaped end winding assembly which is coaxial with, and extends axially from, the stator structure. Typical turbine generator designs employ two coaxial stator coil assemblies with the straight segments of an inner assembly of bottom coils being disposed radially outward from the assembly of top coils in the stator core slots. The end winding segments of the bottom coils are associated in a conical shape which is radially outward from, and coaxial with, the similarly associated conical shape of the end winding segments of the top coils.
Bracing and securing of the end winding assemblies has heretofore been done with conformable pads or blocks located between various support rings. Known support rings extend around the end winding assemblies and are mechanically affixed to brackets which are, in turn, mechanically affixed to the stator core structure for securing the rings, and thus the end windings, in place. Radial clamps banded around the top and bottom coils are also known for providing relatively permanent tightness between the coils. Examples of these known winding supports are those presented in Alkire et al--U.S. Pat. No. 4,387,317 and Cooper et al--U.S. Pat. No. 4,563,607 and U.S. Pat. No. 4,618,795, which are herein incorporated by reference.
However, despite substantial improvements, there is a continuing desire for more reliable end winding support assemblies which minimize excessive vibration, wear of coil insulation, and fatigue cracking of series and copper strand phase connections.
The ring support structure disclosed in Alkire secures the end windings by exerting a radially inward force on the bottom coil and functions in combination with a radial clamp to provide a free-standing, or floating support for the end winding assembly. However, the ring support structure is not supported in any manner such that the entire assembly including the windings and the winding support members remain unsupported. It is known that during abnormal short-circuit operating conditions the forces in the generator tend to expand the windings in a manner which causes fatigue in the ring support members- Thus, since the winding support structure is not supported in any manner, these forces damage the windings and the winding support structure.
The Cooper patents disclose a ring support structure for the stator coils which is mechanically secured to a plurality of braces disposed around the circumference of the end windings. The braces function as a stop to prevent excessive coil deflection during abnormal short circuit operation. The brace is in turn mechanically secured to the stator core such that the winding support structure is firmly secured to the stator core. However, since the brace, and thus the end winding support assembly, is mechanically secured to the stator core, excessive vibration forces are known to cause cracking or abrasion of the end windings and the winding support components. A complex arrangement of cushioning material which forms an elastomer layer and a slip layer is disposed between two segments of the brace in U.S. Pat. No. 4,618,795 in order to decouple the coils from the coil support arrangement. However, this system is complex and costly and the cushion material is known to wear from abrasion over a long period of operation.
Accordingly, there is a need for an end winding support structure which provides reliable support for the end windings of the top and bottom coils and which avoids the problems associated with prior art winding support assemblies. The present invention provides a winding support assembly which satisfies this need.